Recently, onboard information devices that have been developed centering on car navigation systems provide user applications having a variety of radio techniques.
As typical examples of them, a lot of radio communication systems can be mentioned: a system for detecting the vehicle position using a GPS (Global Positioning System), radio beacon or the like; a system for receiving a broadcast such as radio/television; a system for paying a toll using an ETC (Electronic Toll Collection System); a communication system such as a mobile phone and wireless LAN (Local Area Network) for making external communications; and a local radio communication system such as a Bluetooth (registered trademark) for connecting between a user device and an onboard information device. In addition, the ratio of mounting the user applications adopting these radio techniques on the onboard information devices has been increasing.
In the vehicle where the individual radio communication systems mentioned above are mixed, if radio systems using nearby frequency bands are mixed in particular, it is likely that deterioration in communication quality can occur because of radio interference, that is, noise resulting from radio waves used between the radio communication systems.
To circumvent such radio interference conventionally, a local radio communication device for a vehicle has been known which is implemented by using a bandpass filter (BPF) that has transmission spurious emission intensity characteristics with which a radio apparatus will have little effect on the other radio apparatuses among a plurality of onboard radio apparatuses, and by using a bandpass filter (BPF) that has receiving characteristics with which the radio apparatus is free from the effect of the interference due to transmission radio waves from the other radio apparatuses (see, Patent Document 1, for example).
In addition, to prevent communication quality deterioration due to occurrence of radio interference between them when using a radio beacon and a radio wave of an in-vehicle Bluetooth (registered trademark) (near a 2.4 GHz band, for example) at the same time, an onboard communication device is also known which makes a receiving state from a radio beacon station better by stopping communications using the in-vehicle Bluetooth (registered trademark) when detecting that the vehicle approaches the radio beacon station from the radio beacon station position and the vehicle's own position information in car navigation internal information (see Patent Document 2).